Parâmetros para manejo de irrigação e produtividade de gramíneas forrageiras no semiárido mineiro

Abstract

The objective of this study was to determine the crop coefficient, crop evapotranspiration, dry matter yield, water use efficiency and seasonality of four forage grasses in their various stages of development in the four climatic seasons in the semi-arid region of Minas Gerais. We carried out five experiments with four different forages (andropogon, mombaça, tifton-85 and xaraes grasses), managed under cuts in drainage lysimeters. We evaluated four management phases (I, II, III, IV) characterized by age of cuts based on 95% light interception with five replications. The lysimeters allowed to determine the water consumption by the plants, obtained from the difference between the volume applied and the drained one, during each cycle. Water application and drainage were done and measured every two days. The potential reference evapotranspiration was estimated by Penmam-Monteith method, using the data obtained from the automatic meteorological station installed in the experimental area. For the determination of the crop coefficient, the daily values of the reference and the crop evapotranspiration, both in mm.d', were used. The cutting height of "andropogon" grass was of 50 cm, remainin gremaining a residue of 27 cm; the "mombaça" grass of 90 cm, remaininga residue of 45 cm; the tifton-85 grass of 25 cm; remaining residue of 15 cm, and "xaraes" grass of 30 cm, remaining residue of 17 cm. Dry matter production was estimated for each climatic season, in order to identify the degree of production seasonality and the water use efficiency.. The water use efficiency was obtained by dividing the dry matter production by the crop evapotranspiration. The results obtained for the crop coefficient were submitted to analysis of variance and, when significant, to the regression study at 5% probability, with the aid of the SAS program (SAS Institute, 2000). Crop coefficient ranged from 0.70 to 1.25 during summer and fall for all four grasses; in winter / spring, ranging from 0.62 to 1.40, except for "xaraes" grass that ranged from 0.82 to 1.05 in winter and from 0.70 to 0.90 in the spring. Dry matter production was higher in the summer for all grasses studied. The crop evapotranspiration for "andropogon", "mombaça" and tifton-85 grasses was higher in the winter / spring, whereas the "xaraes" grass was larger in the winter, due to the great period without production. The water use efficiency was very low in the winter / spring period for all crops, except for the "xaraés" grass that was in the winter. There was seasonality of production for all the grasses studied, being more accentuated for the 'andropogon' grass.